The present invention relates to aqueous emulsion polymers and coating compositions prepared therefrom.
Aqueous emulsion polymers are well known and have been used in a variety of applications including inks, adhesives, consumer and industrial coatings. A feature of such emulsion polymers is that the polymeric particles in the emulsion generally require some stabilizing mechanism in order to prevent the particles from agglomerating and settling.
One way in which the particles can be stabilized is by incorporating groups into the polymer which generate ions in water whose charges will repel the charges on other polymeric particles. This repulsion prevents the particles from agglomerating. Another way to stabilize polymer particles is through the use of non-ionic surfactants having both hydrophilic and hydrophobic segments which orient in water to form a steric barrier which prevents agglomeration. Additionally, conventional ionic emulsifiers are also used to provide charge repulsion and therefore prevent agglomeration. For example, typical ionic emulsifiers include mono and di-alkyl sulfosuccinates, secondary alkane sulfonates, linear and branched alkylbenzene sulfonates. Often, both ionic and non-ionic mechanisms are used in combination to provide optimum stability.
Conventional non-ionic surfactants are generally water sensitive as a result of the incorporation of oxyethylene units into the surfactant structure. Examples of typical non-ionic surfactants include alkyl aryl ether alcohols based on octyl and nonyl phenol; alkyl aryl polyether alcohols based on octyl and nonyl phenol; alkyl phenol ethoxylates; fatty alcohol ethoxylates; ethylene oxide/propylene oxide copolymers; fatty acid ethoxylates; fatty acid ethylene oxide/propylene oxide copolymers; alkanol amides and ethoxylates and sorbitan esters and ethoxylates.
These approaches, however, are not without attendant difficulties. In coating applications, for example, formulating with such emulsion polymers which make use of these stabilizing mechanisms leads to cured films with increased water sensitivity. This is extremely disadvantageous in applications such as automotive coatings which require good water resistance of the coating.
There is a need, therefore, for a way to prepare aqueous emulsion polymers which are stable and also are capable of providing water resistant films.